It is often difficult to deliver compounds, such as proteins, peptides, genetic material, and other drugs and diagnostic compounds intracellularly because cell membranes often resist the passage of these compounds. Various methods have been developed to administer agents intracellularly. For example, genetic material has been administered into cells in vivo, in vitro and ex vivo using viral vectors, DNA/lipid complexes and liposomes. While viral vectors are efficient, questions remain regarding the safety of a live vector and the development of an immune response following repeated administration. Lipid complexes and liposomes appear less effective at transfecting DNA into the nucleus of the cell and may potentially be destroyed by macrophages in vivo.
Proteins and peptides are typically administered by parenteral administration, or, in some cases, across the nasal mucous membrane. Uptake of drugs administered topically is frequently poor, and degradation frequently occurs when drugs are administered orally. For example, hormones such as gonadotropin releasing hormone ("GnRH") and its analogs have been administered to humans in an attempt to increase fertility by increasing systemic levels of luteinizing hormone ("LH"). When given often, low doses of native GnRH have been shown to induce follicular development and ovulation. These drugs are typically administered via an indwelling catheter into the abdominal cavity. An external pump is attached to the catheter which injects the peptide at frequent intervals. This method of administration is extremely invasive and undesirable. Also, the method is prohibitively expensive for use in animals.
The binding of ligands or assembly proteins to surface receptors of eucaryotic cell membranes has been extensively studied in an effort to develop better ways to promote or enhance cellular uptake. For example, binding of ligands or proteins has been reported to initiate or accompany a cascade of nonequilibrium phenomena culminating in the cellular invagination of membrane complexes within clathrin-coated vesicles [Goldstein, J. L., et al. (1985) Ann. Rev. Cell Biol. 1, 1-39; Rodman, T. S., et al. (1990) Curr. Op. Cell Biol. 2, 664-672; Trowbridge, I. S. (1991) Curr. Op. Cell Biol. 3, 634-641; Smythe, E., et al. (1989) J. Cell Biol. 108, 843-853; Smythe, E., et al. (1992) J. Cell Biol. 119, 1163-1171; and Schmid, S. L. (1993) Curr. Op. Cell Biol. 5, 621-627]. This process has been referred to as receptor-mediatedendocytosis (RME). Beyond playing a central role in cellular lipid trafficking [Pagano, R. E. (1990) Curr. Op. Cell Biol. 2, 652-663], RME is the primary means by which macromolecules enter eucaryotic cells. Having a better understanding of the role of RME in uptake of drugs would be advantageous in developing improved methods of drug delivery.
It would be advantageous to have new methods for delivering agents intracellularly. It is therefore an object of the present invention to provide compositions and methods for enhancing intracellular delivery of bioactive and/or diagnostic agents. It is a further object of the present invention to provide less invasive methods for delivering high molecular weight and labile drugs, such as proteins and nucleic acid molecules, and diagnostic agents.